The planets – With spring come the mighty gas giants (and Mars)

Without a doubt the most crowd-pleasing objects at the telescope eyepiece are the Moon and the large planets Jupiter and Saturn. I can’t tell you how many times I have heard “Oh wow!” and “So cool!” when someone first glimpses one of these objects with their own eyes.

The reason is simple: These objects are bright, show clear structures and detail, and in the cases of Jupiter and Mars are even colorful. Jupiter and Saturn also have bright moons of their own you can spot even with a modest pair of binoculars. For the last few months the planets have been pretty elusive but they are coming back with a vengeance over the next few months. Even tonight, if you get up early enough, before sunrise, you can see Saturn, Mars and Jupiter all in a line (called the ecliptic) in the east.

Jupiter and its moons. Click on image to enlarge.

Let’s take a closer look at each of these targets and get to know them better. Jupiter is currently in Libra and is the highest in the predawn sky. Jupiter is big and bright. It is the fifth planet from the Sun and the largest in the solar system with a mass that is two-and-a-half times that of all the other planets combined. Some have called it a failed star but to put it in perspective it is only 1/1000th the mass of the sun so it had a long way to go before it turned into a star. Jupiter rotates very fast, about 45,000 km/h at the equator, and is bulged out at its middle because of this rapid spinning. A keen observer can notice this at the eyepiece and I have had several people ask me why it isn’t round when observing Jupiter through my telescope. Jupiter is at an average distance from the Sun of around 778 million km and takes nearly 12 years to complete a solar orbit.

Mars and its moons. Click on the image to enlarge.

Next in line we find Mars. Mars is much smaller and harder to spot in the sky. Its tell-tale sign is its color, a coppery reddish hue that stands out from the typically white stars that may be nearby in the sky. The color comes from high iron deposits on the surface that have combined with oxygen to form iron oxide, quite literally rust. Mars is a rocky planet like the Earth but about a third the size, making it the second smallest planet in the solar system, just behind Mercury. Mars is currently in Scorpio, which puts it in the dense star fields of the Milky Way. In small telescopes Mars can be resolved as a reddish disk and when the air is calm with no moon you might be able to glimpse the polar ice caps or some of the surface features, but conditions have to be really good. Mars is the fourth planet from the sun at an average distance of about 230,000,000 Km and an orbital period of just under 687 days. You would be half your age if you lived on Mars! Mars is our best candidate for a long-term extraterrestrial human colony in the solar system because of its size, distance from the sun, and its natural resources.

Saturn and its moons. Click on the image to enlarge.

Last but definitely not least is Saturn. Currently in the constellation Sagittarius, right in the core of the Milky Way, this jewel is the centerpiece of any observing night. Saturn is the sixth planet from the Sun and the second largest in the solar system, after Jupiter. Saturn can currently can be found low in the predawn sky over the eastern horizon. With a large pair of binoculars or a small telescope you can easily see the rings circling this globe, composed mostly of water ice with a little bit of rock and dust thrown in for good measure. The rings extend from 6,630 km to 120,700 km outward from Saturn’s equator, and average only about 20 meters in thickness. This is extremely thin compared to the breadth and width, so when they are tilted edge-on to the earth they basically vanish. The rings change their tilt as seen from Earth over the course of the planet’s orbit, which takes nearly 29.5 years to complete.

Titan, the largest moon in the solar system, is also quite easy to spot somewhere near Saturn, and sharp-eyed observers can spot several more of the 62 known moons. Saturn isn’t the most colorful planet but on good nights the surface looks pale yellow or salmon and, depending on the angle, the rings may cast a dark shadow across its face. Although not nearly as large as Jupiter, Saturn is still a big planet. Its volume is 8.2713×1014 km or about 764 Earth volumes. It is the 6th planet from the Sun and has an average distance of around 1400 million kilometers. If you have never seen this planet with your own eyes, it is well worth the effort to get out and take a look.

Spring is normally known as Galaxy Season but this spring I am going to call it Planet Season since all the interesting planets are grouped pretty closely in the morning sky. As a bonus, if you wait until just before sunrise later in the season, you will also be able to spot Venus and Mercury in the early morning sky. Get out there and let me know which ones you have spotted.

Thanks for reviving my interest in Astronomy Chris. While viewing the moon with my telescope from my driveway after putting it away for many years, my neighbor came out to have a look. He was amazed to see that the moon live looks just like it appears in pictures! Thanks from both of us Chris.

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